1. Field of the Invention
The present invention relates to a liquid crystal display device which mainly performs transmissive display by a backlight and is capable of performing reflective display utilizing external light in a place where illumination of the external light is intense.
2. Description of the Related Art
FIG. 1 is a cross-sectional view showing a configuration of a liquid crystal display device of a first related art. The liquid crystal display device has a configuration, in which a liquid crystal layer 3 is held between an array substrate 1 and an opposite substrate 2, and a backlight 4 is placed on an outside of the array substrate 1.
In the array substrate 1, a polarizing plate 12 is pasted on an outer surface of a glass-made transparent substrate 11 by a transparent adhesive layer 13, an address line 14 is formed on an inner surface of the transparent substrate 11, a transparent insulating layer 15 is formed entirely on the upper surface of the transparent substrate 11, and a pixel electrode 16 and a switching element 17 are formed on an upper surface of the transparent insulating layer 15.
In the opposite substrate 2, a polarizing plate 22 is pasted on an outer surface of a glass-made transparent substrate 21 by a transparent adhesive layer 23, a color filter 24 and a black matrix 25 are formed on an inner surface of the transparent substrate 21, and an opposite electrode 26 is formed so as to cover the color filter 24.
The backlight 4 is a light source using a white LED (Light Emitting Diode). In the case of transmissive display, light emitted by the backlight 4 transmits through the array substrate 1, the liquid crystal layer 3 and the opposite substrate 2 in this order, and is utilized for the display.
Moreover, a reflective layer 41 is formed between the polarizing plate 12 and the backlight 4. In the case of reflective display, light from the outside, such as a sunbeam, is made incident onto a display screen, and transmits through the opposite substrate 2, the liquid crystal layer 3 and the array substrate 1. Then, the light is reflected on the reflective layer 41, transmits through the array substrate 1, the liquid crystal layer 3 and the opposite substrate 2, and is utilized for the display.
However, the first related art has had a problem that a displayed image by the light from the backlight and a reflected image by the light reflected on the reflective layer 41 are overlapped on each other to cause a double image (parallax), leading to deterioration of image quality.
FIG. 2 is a cross-sectional view showing a configuration of a liquid crystal display device of a second related art. In this liquid crystal display device, a light diffusion layer 18 is formed between the transparent substrate 11 and polarizing plate 12 of the array substrate 1 for the purpose of reducing an occurrence of the double image. Other portions are similar to those in FIG. 1. A placement position of the light diffusion layer, usually, should be on the backlight side rather than the liquid crystal layer side when viewed from the display screen side. A reason for this is that, when the light diffusion layer is placed on the display screen side, a character blur owing to light scattering becomes prone to occur on the display screen, leading to the deterioration of the image quality. Note that, as a technology using the light diffusion layer, ones described in Japanese Patent Laid-Open Publication Nos. 2003-255317 and 2003-121847 are known.
FIG. 3 is a cross-sectional view showing a configuration of a liquid crystal display device of a third related art. In this liquid crystal display device, for the purpose of expanding a viewing angle, a viewing angle compensating plate 19 is placed between the transparent substrate 11 and polarizing plate 12 of the array substrate 1, and a viewing angle compensating plate 29 is placed between the transparent substrate 21 and polarizing plate 22 of the opposite substrate 2. This viewing angle compensating plate 19 is pasted on the transparent substrate 11 by the transparent adhesive layer 13 and on the polarizing plate 12 by a transparent adhesive layer 20. Moreover, the viewing angle compensating plate 29 is pasted on the transparent substrate 21 by a transparent adhesive layer 30 and on the polarizing plate 22 by the transparent adhesive layer 23. Other portions are similar to those in FIG. 1.
FIG. 4 is a cross-sectional view showing a configuration of a liquid crystal display device of a fourth related art. In this liquid crystal display device, for both of the purposes of reducing the occurrence of the double image and expanding the viewing angle, the light diffusion layer 18 is placed between the transparent substrate 11 and viewing angle compensating plate 19 of the array substrate 1 in FIG. 3. Other portions are similar to those in FIG. 3. As described above, the fourth related art is one for achieving the reduction of the occurrence of the double image and the expansion of the viewing angle by providing both of the light diffusion layer 18 and the viewing angle compensating plates 19 and 29.
However, though the reduction of the occurrence of the double image is achieved, the fourth related art has had a problem that a contrast ratio is significantly lowered in the case of the transmissive display, resulting in narrowing of a range of the viewing angle.